The US National Archives informed Congress on Sunday that some of Donald Trump's former White House staffers are still in possession of presidential records that are government property.

In a letter dated Friday and made public on late Saturday, acting US archivist Debra Steidel Wall told Representative Carolyn Maloney, a Democrat who heads the House Oversight Committee, "While there is no easy way to establish absolute accountability, we do know that we do not have custody of everything we should."

Although the letter made no mention of who the staffers were, it did say that some used private electronic messaging accounts to conduct official business, hence making it difficult for authorities to access them and to be turned over as required by law.

Wall further spoke of the possibility for the National Archives to consult the Justice Department in order to obtain the documents but did not say that Trump had yet turned over all such documents.

She concluded her letter by referring Maloney to the Justice Department "in light of its ongoing investigation."

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The FBI last month raided Trump’s Mar-a-Lago residence and seized numerous items, including empty folders labeled as "classified", as part of a probe into possible violations of sensitive materials handling protocols. Trump has denied wrongdoing and characterized the investigation as a misuse of the US justice system against him.

Trump has claimed that the documents seized by agents were "all declassified" and that many of the documents were private or covered by the presidential or attorney-client privilege. 

Peter Navarro, a former White House aide, has already been charged with contempt of Congress and subsequently arrested for refusing to cooperate with last year's investigation into the Capitol riot.

The Department of Justice managed to seize all records from him following his arrest on June 4.

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